Author(s): Fiona H. M. Tang; Federico Maggi
Keywords: Nutrient; Flocculation; Kaolinite; Biological matter; Micro-organism
Abstract: The increased mineral fertilizer application rate in agriculture has been identified to result in the leaching of excessive nutrients from land into natural water bodies, to promote growth of aqueous micro-organisms, and to cause eutrophication. These processes not only have large scale repercussions on the ecosystems, but their effects also scale down to the small-scale dynamics of suspended particle matter (SPM) ,eventually affecting the deposition and transport of SPM. The understanding of the SPM response to an increased nutrient load and rapid microbial growth is crucial in monitoring and managing water quality and tracking chemicals and microbially-derived compounds in natural waters. Hence, we present here an experimental facility newly-designed and recently built in the School of Civil Engineering at the University of Sydney, which has been used to investigate the effects of nutrient load on the biological phase of the SPM and, consequently, on SPM flocculation dynamics. This facility is unique as it was designed to allow full control of sediment concentration, nutrient concentration and turbulent shear, and was equipped with an automaticµPIV system to acquire micro photographs of suspended aggregates. In this study, we tested the effects of suspension type (biomass-free or biomass-affected) ,turbulence and sediment concentration on SPM size distribution. Our results show that the presence of nutrients and biological matter in SPM resulted in larger average floc size and higher standard deviation compared to mineral SPM alone. The differences in SPM characteristic between biomass-free and biomass-affected SPM were found to be less pronounced with increasing turbulent shear rate and decreasing sediment concentration.